Field of the Invention
The present invention relates to an organic electroluminescent device (hereinafter, referred to as an “OLED”). More particularly, the present invention relates to an organic electroluminescent device capable of suppressing the spread of ink during the formation of an organic layer using a soluble process to enhance the light-emitting uniformity of a pixel, and a method for fabricating the same.
Discussion of the Related Art
As a core technology in the information communication era, image display devices for implementing various information on a screen thereof have been developed in the direction of high performance while allowing thinner, lighter and portable devices.
As a flat display device capable of reducing the weight and volume, which are the drawbacks of CRTs, an organic electroluminescent device or the like for controlling the light-emitting amount of an organic layer to display an image has been widely used.
The organic light emitting device (OLED) is a spontaneous light-emitting device using a thin light-emitting layer between electrodes, thereby having an advantage of thinning such as a paper.
The organic light emitting device (OLED) having such characteristics may be largely divided into an active matrix OLED (AM-OLED) and a passive matrix OLED (PM-OLED). Here, for the passive matrix OLED (PM-OLED), pixels comprised of 3-color (R, G, B) sub-pixels are arranged in a matrix form to display an image.
Each sub-pixel may include an organic light emitting device and a cell driver for driving the organic light emitting device. The cell driver is configured with a gate line for supplying a scan signal, a data line for supplying a video data signal, and at least two thin film transistors and storage capacitors connected between common power lines for supplying a common power signal to drive an anode of the organic light emitting device.
The organic light emitting device may include an anode, a hole injection layer (HIL), a hole transport layer (HTL), a light-emitting layer, an electron transport layer (ETL), an electron injection layer (EIL), and a cathode.
In particular, the hole injection layer (HIL), hole transport layer (HTL), electron transport layer (ETL) and electron injection layer (EIL) are formed through a soluble process.
Here, when the hole injection layer (HIL), hole transport layer (HTL), electron transport layer (ETL) and electron injection layer (EIL) are formed through the soluble process, a phenomenon such as the spread of solution or the like may be generated, thereby causing a non-uniform thickness of the layers.
From such a point of view, an organic light emitting device according to the related art using a soluble process will be described below with reference to FIGS. 1 and 2.
FIG. 1 is a schematic cross-sectional view illustrating an organic light emitting device according to the related art.
FIG. 2 is a schematic cross-sectional view during the formation of an organic layer according to the related art.
Referring to FIG. 1, a buffer layer (not shown) formed of an insulation material, for example, silicon oxide (SiO2) or silicon nitride (SiNx), which is an inorganic insulation material, is provided on the substrate 11, and a semiconductor layer 13 comprised of a first region 13a forming a channel and second regions 13b, 13c in which a high concentration of impurities are doped on both lateral surfaces of the first region 13a is formed at each pixel region (P) within the display area (AA) at an upper portion of the buffer layer (not shown).
A gate insulating layer 15 is formed on the buffer layer (not shown) including the semiconductor layer 13, and the drive region (not shown) and switching region (not shown) are provided on the gate insulating layer 15, and thus a gate electrode 17 is formed to correspond to the first region 13a of each of the semiconductor layer 13.
Furthermore, a gate line (not shown) connected to a gate electrode 17 formed in the switching region (not shown) and extended in one direction is formed on the gate insulating layer 15.
On the other hand, an interlayer insulating layer 19 is formed on an entire surface of the display area at an upper portion of the gate electrode 17 and gate line (not shown). Here, a semiconductor layer contact hole (not shown) for exposing the second regions 13b, 13c, respectively, located at both lateral surfaces of the first region 13a of each of the semiconductor layer, is provided on the interlayer insulating layer 19 and the gate insulating layer 15 at a lower portion thereof.
Furthermore, a data line (not shown) crossed with a gate line (not shown) to define the pixel region (P) and formed of a second metal material, and a power line (not shown) separated therefrom are formed at an upper portion of the interlayer insulating layer 19 including the semiconductor layer contact hole (not shown). Here, the power line (not shown) may be formed to be separated from and in parallel to the gate line (not shown) on a layer formed with the gate line (not shown), namely, the gate insulating layer.
In addition, a source electrode 23a and a drain electrode 23b brought into contact with the second regions 13b, 13c separated from each other, and respectively exposed through the semiconductor layer contact hole (not shown) and formed of the same second metal material as that of the data line (not shown) are formed in the each drive region (not shown) and switching region (not shown) on the interlayer insulating layer 19. Here, the semiconductor layer 13 and gate insulating layer 15 sequentially deposited on the drive region (not shown) and the gate electrode 17 and interlayer insulating layer 19 and the source electrode 23a and drain electrode 23b formed to be separated from each other form a thin film transistor (T), for example, a drive thin film transistor.
On the other hand, a planarization layer 25 having a drain contact hole (not shown) for exposing the drain electrode 23b of the thin film transistor (not shown) is formed on the thin film transistor and switching thin film transistor (not shown).
Furthermore, a first electrode 29 brought into contact with drain electrode 23b of the drive thin film transistor (not shown) through the drain contact hole (not shown) and having a separated form for each pixel region (P) is formed on the planarization layer 25. Here, the first electrode 29 is hydrophilic and thus organic materials are well stuck thereto.
In addition, an inorganic material is formed on the first electrode 29, and a pixel define layer 33 for separately forming each pixel region (P). Here, the pixel define layer 33 is located between the adjoining pixel regions (Ps) and in addition, part thereof is located at a panel edge portion. The pixel define layer 33 is hydrophobic and thus organic materials are well gathered only within the pixel, and as a result, the organic materials are well placed on the first electrode 29 subsequent to the drying process.
Organic layers 35 formed of organic materials that emit red, green and blue colors, respectively, are formed on the first electrode 29 within each pixel region (P) surrounded by the pixel define layer 33. Here, the organic layers 35 are formed using a soluble process such as an ink-jet printing method to enhance the pattern accuracy.
Furthermore, a second electrode 37 is formed at an upper portion of the organic layer 35 and pixel define layer 33. Here, the first electrode 29, the second electrode 37, and the organic layer 35 interposed between the two electrodes 29, 37 form an organic light emitting device (E).
However, according to an organic light emitting device according to the related art, a bank is configured with a hydrophobic pixel define layer 33 and a hydrophilic first electrode, and in particular, the first electrode 29 is hydrophilic, and thus organic materials are well stuck thereto, but the organic pixel define layer 33 is hydrophobic and thus organic materials are well gathered only within the pixel, and as a result, the organic materials are well placed on the first electrode 29 subsequent to the drying process.
FIG. 2 is a schematic cross-sectional view during the formation of an organic layer according to the related art.
However, as illustrated in FIG. 2, a thickness (t1) variation of the organic layer 35 is generated within the pixel region (P) while an edge area (A) of the organic layer 35 within a pixel is drawn up a sidewall of the pixel define layer 33 during the drying process of the organic layer 35, thereby causing a failure in the edge region of the pixel. In other words, ink bleeding is generated during the ink-jet printing due to the nature of the ink-jet process, and thus a phenomenon occurs in which ink is piled up at a sidewall, namely, an inclined surface of the pixel define layer 33, thereby deteriorating the thickness uniformity of the organic layer within the pixel.
Accordingly, according to an organic light emitting device in accordance with the related art, an organic layer is formed using a soluble process through an ink-jet printing method, and thus a phenomenon occurs in which ink is piled up at a sidewall of the pixel define layer, and consequently the amount of used ink is increased, thereby increasing the fabrication cost of the organic light emitting device.
Furthermore, according to an organic light emitting device in accordance with the related art, a thickness variation of the organic layer is generated within the pixel region while an edge area of the organic layer within a pixel is drawn up a sidewall of the pixel define layer during the drying process of the organic layer, and thus the thickness uniformity of the organic layer is reduced, thereby deteriorating the light-emitting uniformity of the pixel.
In addition, a dry etch or wet etch process is applied during the formation of the pixel define layer in an organic light emitting device according to the related art, and as a result, a damage occurs on a surface of an ITO layer constituting the first electrode, thereby reducing the lifespan of a soluble OLED.